Evolution Lecture No. 33: Social Interactions II
Monday December 3 , 2012
Cooperative Breeding In White-Tailed Bee-Eaters:
-White-tailed bee-eaters live in Africa and are colonial nesters in sandy riverbanks. They live in family
groups of 3-17, where the offspring help at nests (with nest building, nest defense and provisioning).
Conflict Among Kin:
-Conflict among kin describes when parents and offspring disagree about the level of parental care,
leading to parent-offspring conflict. Why does this occur? Well, the coefficient of relatedness is higher
for an offspring conflicting with itself (r = 1) than with siblings (r = 0.5) and parents (r = 0.5) and thus,
conflict among kin can result simply due to a lower relatedness with kin than with the individual itself.
Natural selection should favour offspring who demand greater or longer periods of parental care (they
are fighting for their survival and development more).
POC Over The Duration Of Parental Care:
-By looking at the graph, we see that parent-offspring conflict (POC) occurs because parents are equally
related to their offspring and are therefore expected to equalize their investment among them.
Offspring are only half or less related to their siblings (and fully related to themselves) so they try to get
more parental investment than the parents intended to provide even at their siblings' disadvantage. The
duration of care demanded by the offspring is always going to be longer than the duration of care
provided by the parent.
-Siblicide is better known as the rivalry between siblings that results in one’s death. Masked boobies lay
2 eggs, around 2-10 days apart. When the eggs hatch, the older sibling will often push its younger sibling
out of the nest, which dies of exposure or predation (the parents don’t prevent sibling rivalry attacks). In
blue-footed boobies, the parents lay 2 eggs, over a period of 2-10 days apart and the hatched siblings
may sometimes kill their younger sibling(s). This siblicide depends on food availability and parents often
intervene on the part of the young sibling’s safety. Blue-footed boobies will protect their reproductive
The Reciprocal Transplant Experiment:
-In a reciprocal transplant experiment where treatments of masked booby offspring were raised by blue-
footed booby parents (and vice versa), the degree of siblicide was much higher for masked booby
offspring in blue-footed booby nests. In contrast, the degree of sibilicide was much lower for blue-
footed booby offspring raised in masked booby nests.